Interpreting H₂O isotope variations in high‐altitude ice cores using a cyclone model

Abstract

[1] Vertical profiles of isotope (d 18 O or dD) values versus altitude (z) from sea level to high altitude provide a link to cyclones, which impact most ice core sites. Cyclonic structure variations cause anomalous variations in ice core d time series which may obscure the basic temperature signal. Only one site (Mount Logan, Yukon) provides a complete d versus z profile generated solely from data. At other sites, such a profile has to be constructed by supplementing field data. This requires using the so-called isotopic or d thermometer which relates d to a reference temperature (T). The construction of gapped sections of d versus z curves requires assuming a typical atmospheric lapse rate (dT/dz), where T is air temperature, and using the slope (dd/dT) of a site-derived d thermometer to calculate dd/dz. Using a three-layer model of a cyclone, examples are given to show geometrically how changes in the thickness of the middle, mixed layer leads to the appearance of anomalous d values in time series (producing decalibration of the d thermometer there). The results indicate that restrictions apply to the use of the d thermometer in ice core paleothermometry, according to site altitude, regional meteorology, and climate state.

Eclipse Ice Core Accumulation and Stable Isotope Variability as an Indicator of North Pacific Climate

“…The first ice core record from northwestern North America was recovered in 1980 from the high-elevation location of Mount Logan, Saint Elias Mountains, southwestern Yukon, Canada (Holdsworth et al 1992). Its oxygen isotope record yielded very low correlations with regional station temperature and precipitation due to the distinctly different boundary layer air mass sampled by low-elevation stations (Holdsworth et al 1991(Holdsworth et al , 1992Holdsworth and Krouse 2002). Its oxygen isotope record yielded very low correlations with regional station temperature and precipitation due to the distinctly different boundary layer air mass sampled by low-elevation stations (Holdsworth et al 1991(Holdsworth et al , 1992Holdsworth and Krouse 2002).…”

“…Higher-elevation sites experience a large difference in average d 18 O in zonal versus meridional flow because its moisture source is several thousand kilometers away and can shift dramatically based on the prevailing atmospheric flow pattern. Logan and Eclipse are exposed to different isotopic layers of the troposphere during snowfall events (Holdsworth and Krouse 2002;Holdsworth 2008). Logan around A.D.…”

“…Fisher et al (2008) posited that a quasi-periodic millennial-scale oscillation in the d 18 O and deuterium excess (d) time series are an artifact of oscillating enhanced meridional and zonal North Pacific flow patterns that are responsible for the abrupt drop in values at Mt. Logan (Holdsworth et al 1992;Rupper et al 2004) and the first ice core drilled at Eclipse (1996;Wake et al 2002). 1840A.D.…”

Ice Cores from the St. Elias Mountains, Yukon, Canada: Their Significance for Climate, Atmospheric Composition and Volcanism in the North Pacific Region

“…Our review integrates results from the previous (1996) coring effort conducted at Eclipse Icefield that were not published until after 2000, when analysis of the core began in earnest (Yalcin and Wake, 2001;Wake et al, 2002;Yalcin et al, 2003). The discussion also takes into consideration some new analyses of the NWC ice-core snow accumulation and δ 18 O records published in the past decade (Moore et al, , 2002a(Moore et al, , b, 2003(Moore et al, , 2005Rupper et al, 2004;Holdsworth, 2008;Field et al, 2010). Since 2000, ice cores have been recovered from other areas in the continental northwest Pacific region, including Alaska (Shiraiwa et al, 1999;Urmann, 2009), Kamchatka (Matoba et al, 2007;Yasunari and Yamasaki, 2009), and British Columbia (Neff et al, 2012).…”

“…Logan plateau δ 18 O record (Wake et al, 2002). A step-change in the snow δ 18 O-temperature relationship as a function of altitude is also one of the key features of a cyclone-based isotopic fractionation model developed by Holdsworth (2008) to interpret ice-core paleotemperature histories from highelevation ice cores, including the core from NWC.…”